Konstantinos Nalpantidis

Mid-infrared spectroscopic characterisation of an ultra-broadband tunable EC-QCL system intended for biomedical applications

Mid-infrared spectroscopy has been successfully applied for reagent-free clinical chemistry applications. Our aim is to design a portable bed-side system for ICU patient monitoring, based on mid-infrared absorption spectra of continuously sampled body-fluids. Robust and miniature bed-side systems can be achieved with tunable external cavity quantum cascade lasers (EC-QCL). Previously, single EC-QCL modules covering a wavenumber interval up to 250 cm-1 have been utilized. However, for broader applicability in biomedical research an extended interval around the mid-infrared fingerprint region should be accessible, which is possible with at least three or four EC-QCL modules. For such purpose, a tunable ultra-broadband system (1920 - 780 cm-1, Block Engineering) has been studied with regard to its transient emission characteristics in ns time resolution during different laser pulse widths using a VERTEX 80v FTIR spectrometer with step-scan option. Furthermore, laser emission line profiles of all four incorporated EC-QCL modules have been analysed at high spectral resolution (0.08 cm-1) and beam profiles with few deviations from the TEM 00 spatial mode have been manifested. Emission line reproducibility has been tested for various wavenumbers in step tune mode. The overall accuracy of manufacturer default wavenumber setting has been found between ± 3 cm-1 compared to the FTIR spectrometer scale. With regard to an application in clinical chemistry, theoretically achievable concentration accuracies for different blood substrates based on blood plasma and dialysate spectra previously recorded by FTIRspectrometers have been estimated taking into account the now accessible extended wavenumber interval.

Multivariate Characterization of a Continuous Soot Monitoring System Based on Raman Spectroscopy

The demand for precise and continuous monitoring of air quality has increased. An important descriptor of air quality is the concentration of problematic carbonaceous particles responsible for diseases and climate change. The specific measurement of carbonaceous components in the air is still a topic in research and development. Here, we introduce an integrated and continuous soot monitoring system based on Raman spectroscopy. In comparison to the often utilized light absorption, Raman spectroscopy is capable of determining the graphitic microstructure found in carbonaceous particles. We present first measurements taken in a controlled environment contaminated with varying concentrations of diesel soot. The Raman bands of soot turn out to be tightly mixed up with signals from secondary physical factors. In order to evaluate the data, multivariate methods are applied. After determination of the latent variables using principal component analysis (PCA), the system is further rotated using a linear discriminant analysis (LDA)-criterion and a subsequent nonlinear iterative partial least squares (NIPALS)-like step. One of the variables obtained by this methodology can be shown to exclusively describe the optical filter loading while the orthogonal factor space allows for conclusions on the secondary factors. Copyright 2015 American Association for Aerosol Research

Characterization of a multi-module tunable EC-QCL system for mid-infrared biofluid spectroscopy for hospital use and personalized diabetes technology

Blood glucose monitoring systems are important point-of-care devices for the hospital and personalised diabetes technology. FTIR-spectrometers have been successfully employed for the development of continuous bed-side monitoring systems in combination with micro-dialysis. For implementation in miniaturised portable systems, external-cavity quantum cascade lasers (EC-QCL) are suited. An ultra-broadly tunable pulsed EC-QCL system, covering a spectral range from 1920 to 780 cm-1, has been characterised with regard to the spectral emission profiles and wavenumber scale accuracy. The measurement of glucose in aqueous solution is presented and problems with signal linearity using Peltier-cooled MCT-detectors are discussed. The use of larger optical sample pathlengths for attenuating the laser power in transmission measurements has recently been suggested and implemented, but implications for broad mid-infrared measurements have now been investigated. The utilization of discrete wavenumber variables as an alternative for sweep-tune measurements has also been studied and sparse multivariate calibration models intended for clinical chemistry applications are described for glucose and lactate.

Performance testing of a mid-infrared spectroscopic system for clinical chemistry applications utilising an ultra-broadband tunable EC-QCL radiation source

Mid-infrared (MIR) spectroscopy is a valuable analytical method for patient monitoring within point-of-care diagnostics. For implementation, quantum cascade lasers (QCL) appear to be most suited regarding miniaturization, complexity and eventually also costs. External cavity (EC) - QCLs offer broad tuning ranges and recently, ultra-broadly tunable systems covering spectral ranges around the mid-infrared fingerprint region became commercially available. Using such a system, transmission spectra from the wavenumber interval of 780 to 1920 cm-1, using a thermoelectrically cooled MCT-detector, were recorded while switching the aqueous glucose concentrations between 0, 50 and 100 mg/dL. In order to optimize the system performance, a multi-parameter study was carried out, varying laser pulse width, duty cycle, sweep speed and the optical sample pathlength for scoring the absorbance noise. Exploratory factor analysis with pattern recognition tools (PCA, LDA) was used for the raw data, providing more than 10 significantly contributing factors. With the glucose signal causing 20 % of the total variance, further factors include short-term drift possibly related to thermal effects, long-term drift due to varying atmospheric water vapour in the lab, as well as wavenumber shifts and drifts of the single tuners. For performance testing, the noise equivalent concentration was estimated based on cross-validated Partial-Least Squares (PLS) predictions and the a-posteriori obtained scores of the factor analysis. Based on the optimized parameters, a noise equivalent glucose concentration of 1.5 mg/dL was achieved.

Multi-Step Pattern-Recognition: A Powerful Tool for Substance Identification Based on Real-World Terahertz-Spectra

Combining different chemometric tools we demonstrate the reliable identification of substances out of real-world terahertz-spectra. Systematic evaluation of the spectra allows for the distinction between spectral properties arising from samples geometry versus true material absorption.

Subpicosecond dynamics in calf-thymus DNA, in the presence of Zn 2+ ions: A Raman spectroscopic study

In this paper the Raman total half bandwidths of calf-thymus DNA vibrations have been measured as a function of Zn 2+ ions concentration, in the presence of a constant concentration of Na + ions, respectively. The dependencies of the total half bandwidths and of the global relaxation times, on DNA molecular subgroup structure and on Zn 2+ ions concentration, are reported. It is shown that changes in the subpicosecond dynamics of molecular subgroups in ZnDNA complexes can be monitored with Raman spectroscopy. Particularly, the Raman band parameters for the vibrations at 729 cm −1 (dA), 792 cm −1 (dC, dT and 5 � -C-O-P-O-C-3 � network), 1094 cm −1 (DNA backbone PO2 − symmetric stretching), 1377 cm −1 (dA, dT, dC), 1489 cm −1 (the guanine N-7 and adenine rings) and 1581 cm −1 (dG, dA) of ZnDNA complexes, in the presence of Zn 2+ ions concentrations that varied between 0 and 250 mM, are presented. In our study, the full widths at half-maximum (FWHM) of the bands in calf-thymus DNA complexes are typically in the wavenumber range from 10 to 50 cm −1 . It can be observed that the molecular relaxation processes studied in this work, have a global relaxation time smaller than 0.94 ps and larger than 0.21 ps. The limit values are characterizing the dA and dG residues, respectively (vibrations at 729 cm −1 and 1489 cm −1 ). Binding of Zn 2+ ions to double helical calf-thymus DNA results for some vibrations in smaller global relaxation times and larger bandwidths, respectively, possible as a consequence of the increased interaction of the base moieties with the solvent molecules in unstacked structures. The fastest and the slowest dynamics for different DNA structural subgroups and different Zn 2+ ions concentrations, respec- tively, have been analyzed. A comparison between different time scales of the vibrational energy transfer processes, characterizing the ZnDNA structural subgroups has been given. We have found that metal ions type and concentration are modulators for the (sub)picosecond dynamics of calf thymus DNA molecular subgroups.